Planetary gear apparatus

ABSTRACT

A planetary gear apparatus has an external gear mounted on an input shaft through an eccentric member, and an internal gear which engages with the external gear and is concentric with respect to an output shaft. A recess is provided in the output shaft, and internal or external splines are provided on either the inner or outer side of the recess so as to be concentric with respect to the output shaft. The external gear has either a carrier or an annular groove provided on the side thereof which is closer to the output shaft. The carrier or the annular groove is provided with internal or external splines so as to be concentric with respect to the external gear. The internal or external splines on the output shaft and the internal or external splines on the external gear are operatively connected together by a drive having external or internal splines provided at both ends thereof. The drive is constituted by a hollow shaft having a through-hole. The input shaft is received through the through-hole in the drive and is rotatably born within the recess of the output shaft.

This application is a continuation of application Ser. No. 831,213 filedFeb. 20, 1986, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an improvement in a planetary gearapparatus having an internal gear provided with inner teeth which areconstituted by pins or a combination of pins and rollers, and anexternal gear provided with outer teeth having, for example, atrochoidal tooth form. More particularly, the present invention pertainsto an improvement in a planetary gear apparatus having a joint which isconstituted by a universal joint.

2. Description of the Related Art

A typical conventional planetary gear reducer will first be describedhereinunder, with reference to FIGS. 5 and 6.

The illustrated known planetary gear reducer is arranged so that arotational force imparted from an input shaft 1 is transmitted to anoutput shaft 2 after its rotational speed has been reduced.

The mechanism for reducing the speed is as described below.

Eccentric members 3₁ and 3₂ are provided on the input shaft 1 at apredetermined phase difference (180° in this example). The eccentricmembers 3₁ and 3₂ are in contact with external gears 5₁ and 5₂,respectively, through rollers 4. Each of the external gears 5₁ and 5₂ isprovided with a plurality of inner roller bores 6. An inner pin 7 and aninner roller 8 are fitted into each of the bores 6. The outer peripheryof each of the external gears 5₁ and 5₂ is provided with outer teeth 9having, for example, a trochoidal or circular form. The outer teeth 9engage with outer pins 11 provided on an internal gear 10.

The inner pins 7 are shrink fitted into a flange 12 of the output shaft2.

In this known art, when the input shaft 1 rotates one revolution, theeccentric members 3₁ and 3₂ also rotate one revolution, but the externalgears 5₁ and 5₂ are prevented from self rotating because of theengagement between the inner roller bores 6 and the inner pins 7.Therefore, if the difference between the number of teeth on the externalgears 5₁ and 5₂ and the number of outer pins 11 (acting as inner teeth)is one, when the input shaft 1 rotates one revolution, the externalgears 5₁ and 5₂ move relative to the internal gear 10 only by an amountcorresponding to one outer tooth 9. In consequence, one revolution ofthe input shaft 1 is reduced to an amount through which the externalgears 5₁ and 5₂ turn, which corresponds to the reciprocal of the numberof teeth on the gears 5₁ and 5₂, and the rotational force whose speed isthus reduced is then transmitted to the output shaft 2 through the innerpins 7.

The planetary gear mechanism of the type described above, however,retains the following disadvantages.

The power transmission mechanism which is constituted by the innerroller bores 6, the inner pins 7 and the inner rollers 8 applies aradial force to the output shaft 2. It is therefore necessary to providea flange 12 which is rigid enough to prevent the output shaft 2 frombeing deformed by the application of that force. For this reason, thesize of members or portions near the output shaft 2 cannot be reduced inthe diametrical direction of the shaft 2. In addition, the powertransmission mechanism requires highly-accurate machining and must alsohave a suitably high rigidity, since any slight deformation of a memberor portion thereof has an adverse effect on the operation.

In addition, the inner roller bores 6 occupy a relatively large space inthe external gears 5₁ and 5₂, and therefore hinder any reduction in sizeof the external gears 5₁ and 5₂, which impedes any reduction in the sizeof the apparatus as a whole.

Another type of known mechanism (see the specification of JapanesePatent Application Laid-Open No. 146,939/85) is arranged so that acarrier is mounted on an external gear and is connected to an outputshaft by an intermediate drive gear, whereby radial load is preventedfrom acting on the output shaft. In this apparatus, however, the inputshaft is supported in a cantilever fashion, and this means that thebearing of the shaft must withstand a relatively large load, so that itis not possible to reduce the size of the casing housing the elements onthe input-shaft side.

SUMMARY OF THE INVENTION

In view of the above-described disadvantages of the prior art, it is aprimary object of the present invention to provide an improved planetarygear apparatus that has a simple mechanism which enables the input-shaftside of the apparatus to have a simplified structure and a reduced size,the apparatus further having a reduced axial length and an output-shaftside which also has a simplified structure and reduced size.

To this end, the present invention provides a planetary gear apparatushaving an external gear mounted on an input shaft through an eccentricmember, and an internal gear which engages with the external gear and isconcentric with respect to the output shaft, in which a recess isprovided in the output shaft, and inner or outer splines are provided oneither the inner or outer side of the recess so as to be concentric withrespect to the output shaft. The external gear has either a carrier oran annular groove provided on the side thereof which is closer to theoutput shaft. The carrier or the annular groove is provided with inneror outer splines so as to be concentric with respect to the externalgear. The inner or outer splines on the output shaft and the inner orouter splines on the external gear are operatively connected together bya drive which has outer or inner splines provided at both ends thereof.The drive is constituted by a hollow shaft having a through-hole. Inaddition, the input shaft is received through the through-hole in thedrive and is rotatably born within the recess of the output shaft.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description ofthe preferred embodiments thereof, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of one embodiment of the present invention;

FIG. 2 a sectional view taken along the line B--B of FIG. 1;

FIGS. 3 and 4 sectional views showing in combination another embodimentof the present invention;

FIG. 5 is a sectional view of a one example of conventional apparatus;and

FIG. 6 is a sectional view taken along the line A--A of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described hereinunder in detail withreference to the accompanying drawings.

Referring first to FIGS. 1 and 2 which show in combination oneembodiment of the present invention, an input shaft 21 is formed with aneccentric member 22 having an eccentricity e. An external gear 24 isfitted on the eccentric member 22 through a bearing 23. Accordingly, theexternal gear 24 is disposed in such a manner that the axis 0₂ of theexternal gear 24 is eccentric with respect to the axis 0₁ of the inputshaft 21 (and also an internal gear 26) by the eccentricity e. Outerteeth 25 of the external gear 24 have an appropriate tooth form such asa trochoidal or circular tooth form. The outer teeth 25 engage withinner teeth of the internal gear 26 which are constituted by outer pins27. The external gear 24 has a carrier 28 integrally provided on theside thereof which is closer to an output shaft 30. The carrier 28 isprovided with inner splines 29 which are concentric with respect to theexternal gear 24.

The output shaft 30 is provided with a recess 31. The inner side of therecess 31 is provided with inner splines 32 which are concentric withrespect to the input shaft 21. A floating drive 35 which has outersplines 33 and 34 is supported between the inner splines 29 and 32.

The drive 35 is constituted by a hollow shaft having a through-hole 36defined therein. The input shaft 21 is received through the through-hole36 and is rotatably supported by a bearing 37 within the recess 31 ofthe output shaft 30. Accordingly, the input shaft 21 is supported at twoportions on both sides of the external gear 24 by the bearing 37 and 38,respectively.

The internal gear 26 is tubular and integral with an output-shaft casingand is secured to an input-shaft casing 39 by bolts 40. The output shaft30 is rotatably supported by the output-shaft casing integral with theinternal gear 26 through bearings 41.

Another embodiment of the present invention is shown in FIGS. 3 and 4.Since this embodiment is basically the same as the first embodimentshown in FIGS. 1 and 2, the same constituent elements or portions ofthis embodiment as those of the first embodiment are denoted by the samereference numerals, and description will be made with respect to onlydifferencies between these embodiments.

In this embodiment, in place of the carrier 28, an annular groove 42 isprovided on the side of the external gear 24 which is closer to theoutput shaft 30. The annular groove 42 is provided with inner splines 43which are concentric with respect to the external gear 24. On the otherhand, the output shaft 30 is provided with a recess 31 which is providedon the outer side thereof with outer splines 44 which are concentricwith respect to the input shaft 21. In addition, a floating drive 47which has outer and inner splines 45 and 46 is floating between theinner and outer splines 43 and 44.

The following is a description of the operation of the planetary gearapparatus according to the present invention, arranged as describedabove.

As the input shaft 21 rotates, the eccentric member 22 also rotates, sothat a rotational force imparted from the input shaft 21 is transmittedto the external gear 24 through the bearing 23. Since the axis 0₁ of theinput shaft 21 and the axis 0₂ of rotation of the external gear 24 areeccentric with respect to each other by the eccentricity e and theexternal gear 24 is operatively connected to the floating drive 35 or 47through either the carrier 28 or the annular groove 42, the revolutionof the external gear 24 around the axis 0₁ of the input shaft 21 isabsorbed by the oscillation of the drive 35 or 47, and the rotationalforce from the input shaft 21 alone is taken out after its rotationalspeed has been reduced to the reciprocal of number of outer teeth 25because of the engagement between the external gear 24 and the outerpins 27. The rotational motion of the external gear 24 is transmitted tothe drive 35 or 47 through the carrier 28 or the annular groove 42 andis further transmitted to the output shaft 30.

The load which acts on the input shaft 21 is applied thereto through theexternal gear 24. However, since the input shaft 21 is supported at twoportions on both sides of the external gear 24 by the bearings 37 and38, respectively, a correspondingly reduced load is applied to each ofthe bearings 37 and 38, and this means that it is possible to reduce thesize of the bearings 37 and 38.

Although the present invention has been described above with respect toa gear reducer, it is to be noted here that the invention may also beapplied to a speed increaser.

The present invention, which is arranged and operates as describedabove, offers the following various advantages.

Since the input shaft is supported at two portions on both sides of theexternal gear, it is possible to reduce the size of the bearings whichrotatably support the input shaft, so that each of the input shaft andthe input-shaft casing is allowed to have a reduced size and asimplified structure.

The drive which is constituted by a hollow shaft enables a reduction inweight of the apparatus as a whole.

Since the drive is supported in such a manner that it floats withrespect to the carrier or the annular groove of the external gear andthe output shaft, any possible machining error can be absorbed, so thatthere is no need for a specially high degree of accuracy in machining.

The present invention needs no inner roller bores. Therefore, thediameter in the radial direction of the external gear can be minimized,so that it is possible to obtain a reduction gear apparatus with areduced size.

Since torque alone is transmitted to the output shaft and no radial loadacts thereon, it is possible to reduce any angular back-lash which maybe generated as a result of deformation of the output shaft.

The internal gear which is tubular and integral with the output-shaftcasing enables the output-side of the apparatus to have a reduced sizeand a simplified structure and permits transmission of large torque,since there is no connection by means of a bolt.

What is claimed is:
 1. In a planetary gear apparatus having: an input shaft; an eccentric member mounted on said input shaft so as to be eccentric with respect to said input shaft; a stationary internal gear concentrically surrounding said input shaft; an external gear carried by said eccentric member and engaging with said internal gear, said external gear rotating around its own axis while revolving around the axis of said input shaft in response to the rotation of said input shaft; an output shaft extending coaxially with respect to said input shaft; and a driving member which connects together said external gear and said output shaft to transmit the rotational motion of said external gear to said output shaft,an improvement comprising: said output shaft being provided at one end thereof with a recess which surrounds the distal end portion of said input shaft; said driving member being constituted by a hollow shaft having a through-hole through which said input shaft extends, said hollow shaft having both end portions thereof operatively connected to said external gear and said output shaft through splines, respectively; and said input shaft having its distal end portion rotatably born within the recess in said output shaft.
 2. In a planetary gear apparatus having an external gear mounted on an input shaft through an eccentric member, and a stationary internal gear which engages with said external gear and is concentric with respect to an output shaft,an improvement comprising: a recess provided in said output shaft; a carrier provided on said external gear; a drive member spline connected at one end thereof to said output shaft and spline-connected at the other end thereof to said carrier, said drive member being constituted by a hollow shaft having a through-hole, said input shaft being received through the through-hole of said drive member and rotatably born within the recess of said output shaft.
 3. The improvement of claim 2, wherein internal splines are provided on an inner surface of a first portion of said recess of said output shaft concentric with said output shaft and said input shaft is rotatably born in a second portion of said recess axially spaced from said first portion, further internal splines are provided on said carrier concentric with respect to said external gear, and said drive member is provided with external splines at both ends thereof meshing together with said internal splines of said output shaft and said further internal splines of said carrier.
 4. In a planetary gear apparatus having an external gear mounted on an input shaft through an eccentric member, and a stationary internal gear which engages with said external gear and is concentric with respect to an output shaft,an improvement comprising: a recess provided in said output shaft; an annular groove provided on the side of said external gear which is closer to said output shaft; a drive member spline-connected at one end thereof to said output shaft and spline-connected at the other end thereof to said annular groove, said drive member being constituted by a hollow shaft, said input shaft being received through the hollow portion of said drive member and rotatably born within the recess of said output shaft.
 5. The improvement of claim 4, wherein external splines are provided on an external surface of said output shaft concentric with said output shaft, internal splines are provided on a surface of said annular groove of said external gear concentric with an axis of said external gear, and said drive member is aprovided with internal splines at one end thereof meshing with said external splines of said output shaft and external splines at the other end thereof meshing with said internal splines of said external gear. 